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Authentication Protocol

A mechanism for verifying the identity of a user or device attempting to access a network resource, typically using passwords or certificates.
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The statement of the theorem

Let UU be the user, AA be the authenticator, and SS be the shared secret key. Define the authentication protocol Auth(U,A,S)\text{Auth}(U, A, S) as a challenge-response mechanism. The protocol verifies identity if and only if the response RR generated by AA to a challenge CC satisfies the condition: Verify(C,R,S)=True\text{Verify}(C, R, S) = \text{True}, where Verify\text{Verify} is a function that confirms RR is derived from CC using SS, and Pr(Verify(C,R,S)=True∣A is not U)≈0\text{Pr}(\text{Verify}(C, R, S) = \text{True} | A \text{ is not } U) \approx 0.